Hinged closures, also referred to as "flip top" closures incorporate a base and a lid. The base is adapted to engage a closure, and incorporates a top surface having an opening. The lid is attached to the base by a connection such as a hinge so that the lid is movable, relative to the base, between closed and open positions. In the closed position, the lid overlies the top surface of the base and occludes the opening, whereas in the open position the lid is remote from the opening. When the base is secured to the mouth of a container, the lid controls access to the contents of the container. The base, lid and hinge may be molded as elements of a single, integral piece of plastic material.
Various attempts have been made to provide child resistant flip top closures having features which impede opening of the lid by a child but which permit opening of the lid by an adult. Such child-resistant features are useful where the closure is employed on a container holding a toxic: or otherwise hazardous material.
British patent application No. 2 158 048 A discloses a flip top cap having a ring movably mounted to the base. In the normal position of the ring, the ring protrudes upwardly from the base and surrounds the lid when the lid is in the closed position. Thus, the periphery of the lid is inaccessible, and a child cannot engage the lid to move it from the closed position to the open position. An adult can move the ring downwardly relative to the base so as to gain access to the lid, but a child normally cannot accomplish the required twisting and sliding motion. The closure shown in U.S. Pat. No. 3,584,760, utilizes a guard ring rotatable relative to the base with a separate spring for biasing the guard ring. These features add cost and complexity to such a device, and, significantly, suffer from the disadvantage that the covering member must be physically manipulated back from the uncovered to the covered position. In other words, without such manipulation after use of the closure, the container contents remain accessible to children.
Others have attempted to make a satisfactory child resistant flip top closure having all of its elements molded in a single piece. As disclosed in U.S. Pat. Nos. 3,556,331 and 3,604,585, the lid may have an elongated, rectangular shape, whereas the base may have a narrow slot in its top surface. When the lid is in its closed position, it is recessed within the slot in the top surface of the base. The parts are dimensioned so as to provide only a very narrow opening at the end of the lid remote from the hinge so that the lid can be opened only by an adult capable of engaging a tool or fingernail within this narrow opening. U.S. Pat. No. 4,047,495 describes a child resistant closure wherein the base is provided with an upstanding rim or wall around its top surface, such that the lid is recessed within this rim when in the closed position. The base is also provided with a projection adjacent the middle of the top surface so that the underside of the lid bears on the projection. The lid can be opened by forcing its rearward portion, adjacent the hinge, downwardly, towards the base. The projection on the base acts as a fulcrum, causing the forward portion of the lid to lift upwardly and hence to project above the rim on the base. In this condition the forward portion of the lid can be engaged and pulled upwardly, away from the base so as to swing the lid to its open position U.S. Pat. No. 4,371,095 utilizes a similar arrangement. U.S. Pat. No. 4,533,058 employs an elongated, strap-like lid received in an elongated slot extending entire across the top surface of the base from the rear or hinge side to the front side. The base is provided with a cam surface such that when the distal portion of the strap-like lid, remote from the hinge, is forced downwardly, the tip of the lid is forced outwardly at the front cf base. The outwardly projecting tip can be engaged and pulled upwardly.
U.S. Pat. No. 4,444,326 discloses a flip top closure having a base integral with the container body itself and incorporating a peripheral wall on the base which can be forced inwardly at one location so as to expose the underside of the lid for manual engagement. U.S. Pat. No. 4,209,100 shows a further child resistant closure having a lid which recessed in the top surface of the base when the lid is in the closed position. The base has an upstanding peripheral wall abutting the forward portion of the lid, remote from the hinge. This peripheral wall is arranged so that it can be forced inwardly, towards the lid. The lid and peripheral wall are provided with cam surfaces so that inward motion of the peripheral wall will move the lid upwardly, away from its closed position to a partially open position. In this partially open position, the lid protrudes above the top surface of the base and hence is accessible for manual engagement by the user.
A further child resistant closure is disclosed in U.S. Pat. No. 3,826,394. The closure of the U.S. Pat. No. 3,826,394 includes a lid having a projection at the distal extremity of the lid, remote from the hinge. The projection extends forwardly adjacent the forward edge of the base when the lid is in the closed position. A pair of guard members mounted on the forward edge of the base define a vertically extensive slot. The projection on the distal end of the lid is disposed in the slot when the cap is in the closed position. In some embodiments of the U.S. Pat. No. 3,826,394 closure, such as those shown in FIGS. 4-6 and 7-9 thereof, a flat, plate-like tab extends between the guard members or projects upwardly in the slot between the guard members. The tab confronts the distal extremity of the projection on the lid. To open the lid, the tab is flexed forwardly and hence away from the lid and a finger or fingernail is inserted under the projection.
Each of the aforementioned closures leaves something to be desired with respect to resistance to opening by a child, ease of opening by an adult, manufacturing cost, appearance and other important factors. Despite the extensive efforts made by the art heretofore towards development of a truly satisfactory child resistant flip top closure, there remains a need for still further improvements.